SpaceX test flight: can a rocket be landed back on Earth?

A groundbreaking rocket launch by private space exploration company SpaceX and Nasa has been postponed until Friday, due to a last-minute fault.

Falcon 9 will be carrying vital cargo to the International Space Station (ISS), but scientists are also hoping to make a historic rocket landing when the mission returns to Earth, which could have huge impacts for commercial space travel.

What will happen?

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The main mission is to send a capsule filled with supplies of food, water and materials to the ISS, but an unprecedented feat will also be attempted once the capsule disengages from the rocket that propelled it into space - getting the rocket back to Earth in one piece so it can be re-used.

As the rocket descends at almost a mile a second, the engine will relight three times in order to adjust the point of impact and slow it down, The Guardian reports. Fins on the side of the rocket will also deploy as scientists try to land the unit on a giant floating platform in the middle of the Atlantic Ocean.

Will it succeed?

According to the company, stabilising the rocket for re-entry will be "like trying to balance a rubber broomstick on your hand in the middle of a wind storm".

The company has been playing down expectations of the mission, says the BBC, suggesting that there is only a 50 per cent chance of success. "I'm pretty sure this will be very exciting, but, as I said, it's an experiment," warned Hans Koeningsman, the firm's vice president for mission assurance.

"There's a certain likelihood that this will not work out all right, that something will go wrong. It's the first time we have tried this – nobody has ever tried it as far as we know," he added.

Why is it so significant?

If scientists are able to retrieve the rocket and reuse it, it would herald a major breakthrough in space travel. Rocket components are normally discarded after use as they get damaged upon their return to Earth. Reusable rockets would significantly reduce the launch costs of future missions, making them more accessible to governments, private firms and even individuals.

"The reason that there's low demand for spaceflight is that it's ridiculously expensive," said SpaceX founder Elon Musk. "These spaceships are expensive and they're hard to build," he said. "You can't just leave them there."